1. Field of the Invention
The present invention relates to a chroma signal decimation filter device for removing sampled data from the chrominance component of a digital video signal and a chroma signal interpolation filter device for interpolating the sampled data using their adjacent data.
2. Description the Prior Art
For reducing the data of a video signal to a desired size for ease of recording or transmission, a method of decimation of horizontal or vertical sample data of the signal is commonly employed. While the amount of data of a signal for recording or transmission is decreased its frequency band to be reproduced is less than a particular (or Nyquist) frequency which has a wavelength which is two times the sampling period. If the frequency band before sampling exceeds the Nyquist frequency, aliasing distortion will appear thereby reducing the quality of a reproduced image. The Nyquist theorem suggests that the sampled data dropped by decimation will be restored through filtering them to pass only a Nyquist bandwidth portion.
The aliasing distortion is undesired in visual reproduction and must be eliminated by reducing, prior to data decimation, the bandwidth of a signal to less than the Nyquist frequency with a lowpass filter in a conventional signal decimation device. For interpolation of a data portion below the Nyquist frequency, the same lowpass filter for limiting a bandwidth to less than the Nyquist frequency can be used. More specifically, all the frequency components below the Nyquist frequency can be decoded with the LPF which is thus desirable for use as an interpolation device.
It is known that the visual sensitivity of human eyes is not high to a chrominance signal as compared with a luminance signal and also, high frequency components are less sensitive than low frequency components. Accordingly, the technique of decimating the chrominance components is preferred for reducing the amount of data of a video signal. Such devices for limiting the band of the chrominance components to a suitable width for decimation and interpolation are known as a chroma signal decimation filter device and a chroma signal interpolation filter device.
However, known chroma signal decimation and interpolation filter devices are not capable, never in theory, of reproducing a frequency band more than the Nyquist frequency. For example, an image data which contains an elaborate picture pattern of colors can be processed by the known chroma signal decimation and interpolation filter devices with the development of undesired color fringing.